A National Weather Service fire weather watch for the inland valleys and the mountains will take effect at 3 a.m. Thursday and extend through 3 p.m. Saturday.
Northeast winds of 15 to 25 miles per hour with gusts of up to 40 mph are expected to develop early Thursday and continue through Saturday afternoon. Forecasters said they would begin in the Santa Ana mountains and parts of the Inland Empire, then spread to San Diego County's coastal slopes and foothills on Friday.
Low humidity and somewhat elevated temperatures are also expected.
“The heat will not be excessive, but after a bout of cool days, the change will be quite noticeable with temps reaching into the 90s across much of the inland valley regions by Friday and reaching into the 80s even near the coast,'' according to the weather service.
Forecasters said the combination of gusty winds, low humidity and dry fuels would result in critical fire weather conditions.
The winds are expected to weaken by Sunday, but warm and dry weather will persist into early next week.
“The most widespread critical fire weather conditions will exist Friday morning into early Friday afternoon as offshore winds peak and very dry conditions persist,'' according to the weather service. “Winds will weaken for Saturday, with much lighter winds and some improvement in humidity on Sunday.''